linux-kernel - Re: [PATCH v4 3/6] KVM: arm64: Implement kvm_arch_flush_remote_tlbs

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Message-ID: <87v8gbjkzn.wl-maz@kernel.org>
Date:   Mon, 29 May 2023 15:00:28 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 3/6] KVM: arm64: Implement kvm_arch_flush_remote_tlbs_range()

On Fri, 19 May 2023 01:52:28 +0100,
Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> 
> Implement kvm_arch_flush_remote_tlbs_range() for arm64
> to invalidate the given range in the TLB.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  3 +++
>  arch/arm64/kvm/hyp/nvhe/tlb.c     |  4 +---
>  arch/arm64/kvm/mmu.c              | 11 +++++++++++
>  3 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 81ab41b84f436..343fb530eea9c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1081,6 +1081,9 @@ struct kvm *kvm_arch_alloc_vm(void);
>  #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
>  int kvm_arch_flush_remote_tlbs(struct kvm *kvm);
>  
> +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages);
> +
>  static inline bool kvm_vm_is_protected(struct kvm *kvm)
>  {
>  	return false;
> diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
> index d4ea549c4b5c4..d2c7c1bc6d441 100644
> --- a/arch/arm64/kvm/hyp/nvhe/tlb.c
> +++ b/arch/arm64/kvm/hyp/nvhe/tlb.c
> @@ -150,10 +150,8 @@ void __kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
>  		return;
>  	}
>  
> -	dsb(ishst);
> -
>  	/* Switch to requested VMID */
> -	__tlb_switch_to_guest(mmu, &cxt);
> +	__tlb_switch_to_guest(mmu, &cxt, false);

This hunk is in the wrong patch, isn't it?

>  
>  	__flush_tlb_range_op(ipas2e1is, start, pages, stride, 0, 0, false);
>  
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index d0a0d3dca9316..e3673b4c10292 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -92,6 +92,17 @@ int kvm_arch_flush_remote_tlbs(struct kvm *kvm)
>  	return 0;
>  }
>  
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages)
> +{
> +	phys_addr_t start, end;
> +
> +	start = start_gfn << PAGE_SHIFT;
> +	end = (start_gfn + pages) << PAGE_SHIFT;
> +
> +	kvm_call_hyp(__kvm_tlb_flush_vmid_range, &kvm->arch.mmu, start, end);

So that's the point that I think is not right. It is the MMU code that
should drive the invalidation method, and not the HYP code. The HYP
code should be as dumb as possible, and the logic should be kept in
the MMU code.

So when a range invalidation is forwarded to HYP, it's a *valid* range
invalidation. not something that can fallback to VMID-wide invalidation.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.